Monitoring Glacier and Supra-glacier Lakes from Space in Mt. Qomolangma Region of the Himalayas on the Tibetan Plateau in China

Because of the large number and remoteness, satellite data, including microwave data and optical imagery, have commonly been used in alpine glaciers surveys. Using remote sensing and Geographical Information System （GIS） techniques, the paper presents the results of a multitemporal satellite glacier extent mapping and glacier changes by glacier sizes in the Mt. Qomolangma region at the northern slopes of the middle Himalayas over the Tibetan Plateau. Glaciers in this region have both retreated and advanced in the past 35 years, with retreat dominating. The glacier retreat area was 3.23 km2 （or o.75 km^2 yr^-1 during 1974 and 1976, 8.68 km^2 （or 0.36 km^2 yr^-1 during 1976 and 1992, 1.44 km^2 （or 0.12 km^2 yr^-1） during 1992-2ooo. 1.14 km^2 （or 0.22 km^2 yr^-1 during 2000-2003, and 0.52 km^2 （or 0.07 km^2 yr^-1 during 2003-2008, respectively. While supra-glacier lakes on the debris-terminus of the Rongbuk Glacier were enlarged dramatically at the same time, from 0.05 km^2 in 1974 increased to 0.71 km^2 in 2008, which was more than 13 times larger in the last 35 years. In addition, glacier changes also showed spatial differences, for example, glacier retreat rate was the fastest at glacier termini between 5400 and 5700 m a.s.l than at other elevations. The result also shows that glaciers in the middle Himalayas retreat almost at a same pace with those in the western Himalayas.

Spatial and Temporal Dynamics of Lakes in Nam Co Basin, 1991–2011

Lakes in Tibet Plateau with little effects of human activities serve as important indicators of climate change. This study analysed remote sensing data and long term climate variables to examine the hydrological response of lakes in Nam Co Basin. The area changes of lakes were extracted by Landsat TM/ETM＋ and analysed by SRTM 3 DEM. And the ICESat elevation data between 2003 and 2009 were used to observe the lake level of the Nam Co Lake. The results show that the number of new formed glacier lakes increased by 36% and the area of glacier lakes increased by 36.7%（0.97 km^2） from 1991 to 2011. At the same time, the surface area of the Nam Co Lake expanded by 3.71%（72.64 km^2） of the original size in 1991, with a tendency value of 3.63 km^2 per year. The lake level of the Nam Co Lake shows an increase tendency of 0.24 m per year during 2003-2009. These variations appear to be related to an increase in mean annual temperature of 0.06 oC per year, and an increase in annual precipitation of 2.1 mm per year in summer in the last two decades. The increased number of lakes and increased area of glacial lakes reached a peak at an altitude of 5 500-5 600 m a.s.l.. The number of new formed glacier lakes and the area of glacier lakes tend to higher altitudes. Climate change has an important impact on the variation of the glacier lakes and the Nam Co Lake.

The response of lake-glacier variations to climate change in Nam Co Catchment, central Tibetan Plateau, during 1970-2000

Based upon the 1970 aero-photo topographic map, and TM/ETM satellite images taken in 1991 and 2000, the authors artificially interpreted boundaries of lake and glaciers in Nam Co Catchment, and quantified lake-glacier area variations in different stages by ＂integrated method＂ with the support of GIS. Results show that from 1970 to 2000, lake area increased from 1942.34 km^2 to 1979.79 km^2 at a rate of 1.27 km^2/a, while glacier area decreased from 167.62 km^2 to 141.88 km^2 at a rate of 0.86 km^2/a. The increasing rate of lake in 1991-2000 was 1.76 km^2/a that was faster than 1.03 km^2/a in 1970-1991, while in the same period of time, the shrinking rates of glaciers were 0.97 km^2/a and 0.80 km^2/a respectively. Important factors, relevant to lake and glacier response to the climate, such as air temperature, precipitation, potential evapotranspiration and their values in warm and cold seasons, were discussed. The result suggests that temperature increasing is the main reason for the accelerated melting of glaciers. Lake expansion is mainly induced by the increase of the glacier melting water, increase of precipitation and obvious decrease of potential evapotranspiration. Precipitation, evaporation and their linkages with lake enlargement on regional scale need to be thoroughly studied under the background of global warming and glacier retreating.

Quantitative analysis of lake area variations and the influence factors from 1971 to 2004 in the Nam Co basin of the Tibetan Plateau

By using remote sensing and GIS technologies, spatial analysis and statistic analysis, we calculated the water area and volume variations of the Nam Co Lake from 1971-2004, and discussed their influence factors from the viewpoints of climatic change and water balance. Data source in this study includes bathymetric data of the lake, aerial surveyed topographic maps of 1970, remote sensing images of 1991 and 2004 in the lake catchment, meteorological data from 17 stations within 1971-2004 in the adjacent area of the lake catchment. The results showed that the lake area expanded from 1920 km2 to 2015 km2 during 1971 to 2004 with the mean annual increasing rate (MAIR) of 2.81 km2 a-1, and the lake volume augmented from 783.23×108 m3 to 863.77×108 m3 with the MAIR of 2.37×108 m3. Moreover, the MAIR of the lake area and volume are both higher during 1992 to 2004 (4.01 km2 a-1 and 3.61×108 m3 a-1) than those during 1971 to 1991 (2.06 km2 a-1 and 1.60×108 m3 a-1). Analyses of meteorological data indicated that the continue rising of air temperature conduced more glacier melting water. This part of water supply, together with the increasing precipitation and the descending evaporation, contributed to the enlargement of Nam Co Lake. The roughly water balance analyses of lake water volume implied that, in two study periods (1971-1991 and 1992-2004), the precipitation supplies (direct precipitations on the lake area and stream flow derived from precipitations) accounted for 63% and 61.92% of the whole supplies, while the glacier melting water supplies occupied only 8.55% and 11.48%, respectively. This showed that precipitations were main water supplies of the Nam Co Lake. However, for the reason of lake water increasing, the increased amount from precipitations accounted for 46.67% of total increased water supplies, while the increased amount from glacier melting water reached 52.86% of total increased water supplies. The ratio of lake evaporation and lake volume augment showed that 95.71% of total increased water supplies contributed to the augment of lake volume. Therefore, the increased glacier melting water accounted for about 50.6% of augment of the lake volume, which suggested that the increased glacier melting water was the main reason for the quickly enlargement of the Nam Co lake under the continuous temperature rising.

Relationship between Land Cover Changes with Water Quantity in Lake Victoria—A Case Study of Mara River Basin in Tanzania

LV(Lake Victoria)is valuable to the East African sub region and Africa in general,sources of water for LV are from its catchment areas and tributaries e.g.Kagera and Mara Rivers on Tanzania part.Apparently,catchment areas in proximities of LV and on MR(Mara River),indeed on MRB(Mara River Basin)in particular,are experiencing increased anthropogenic activities such as mining,fishing,settlements,agriculture etc.,which lead to increased water usage,land degradation and environmental pollution.Such activities threaten the sustainability of the environment surrounding MRB and impliedly LV and its ecosystem.The level of water in LV is reported to be declining threatening its extinction.This paper is reporting on a study undertaken to establish the relationship between land cover changes with ground water discharge from specifically MRB into LV over the period of 24 years,i.e.1986 to 2010.Methodology used is assessment of vegetation changes by using remote sensing through analysis of TM(Thematic Mapper)Landsat Images of 1986,1994,2002 and 2010 ETM(Enhanced Thematic Mapper)Landsat images,from which respective land cover change maps were generated and compared with ground water levels from MRB.Results indicates that there is a significant decline of land cover and ground water flowing into LV from MRB,and that there is positive correlation between land cover changes and the quantity of ground water flowing from MRB to LV.This phenomenon is common to all tributaries of LV,thus leading to decline of water in LV.It is recommended that relevant government institutions should endeavor formulating policies to control excessive use of wetlands and drylands in the proximity of LV and MRB in particular,such that the flow of water to LV may be sustained.

Response of Lakes to Climate Change in Xainza Basin Tibetan Plateau Using Multi-Mission Satellite Data from 1976 to 2008

Changes in the lake areas of Xainza basin in the past 33 years （1976 to 2008） were studied using Landsat data from Multispectral Scanners （1973- 1977）, Thematic Mapper （1989-1992, 2007-2009）, and Enhanced Thematic Mapper Plus （1999-2002）. The results indicated that lakes in the study area evidently expanded from 1976 to 2008, with total expansion of 1512.64km2. The mean annual air temperature presented an upward trend with certain fluctuations from 1966 to 2008. The air temperature rise rates in the cold season （o.31~C/loa） were higher than those in the hot season （0.24℃/1oa）, in the Xainza station example. Precipitation exhibited evident seasonal differences. Mean annual precipitation in hot season is 281.48 mm and cold season is 32.66 mm from 1966 to 2008 in study area. Precipitation in the hot season was the major contributor to the increase in annual precipitation. Grey relational analysis （GRA） was used to study the response of lake areas to climatic factors. The mean air temperature and precipitation were selected as comoared series, and the lake areas were regarded as the reference series. The grey relational grade （GRG） between compared series and reference series were calculated through GRA. The results indicated that changes in lake areas were mainly affected by climatic factors in the hot season. Lakes in this region were classified into three grades, namely, Grades I, II, and III according to the recharge source and elevation. The GRGs of each series varied for different grade lakes： the area of Grade III lakes were the most relevant to the hot season factors, the GRGs of precipitation and air temperature were 0.7570 and 0.6606; followed by the Grade II lakes; Grade I lakes were more sensitive to the air temperature.

Glacier in the upstream Manla Reservoir in the Nianchu River Basin,Tibet:shrinkage and impacts

Glaciers in the upstream Mania Reservoir in the Nianchu River Basin are crucial for agriculture and hydropower in the ＂One River and Two Streams＂ area. Rising temperature has caused widespread retreat of glaciers on the Tibetan Plateau during the last few decades. In this study, glacier variations under climate change in the Nianchu River Basin are quantified and their influence are evaluated by analyzing 1980 aerial topographic maps, 1990 Landsat TM, 2000 Landsat ETM＋, and 2005 CBERS remotely sensed images. It is found that from 1980 to 2005, the debris-free glacier area shrank by 7.3% （13.42 kin2）. Glacier shrinkage will have a positive effect on agriculture, hydropower and eco-environment in the near future. However, because the large number of small glaciers （〈2 km2） will rapidly retreat and disappear in future years, melt water will decrease, ultimately resulting in a long term water shortage. Glacial lakes exhibited rapid expansion due to accelerating glacier retreat during 19802005, increasing the possibility of glacial lake outbtwst floods.

Response of glacier area variation to climate change in the Kaidu-Kongque river basin,Southern Tianshan Mountains during the last 20 years

Glaciers are crucial water resources for arid inland rivers in Northwest China.In recent decades,glaciers are largely experiencing shrinkage under the climate-warming scenario,thereby exerting tremendous influences on regional water resources.The primary role of understudying watershed scale glacier changes under changing climatic conditions is to ensure sustainable utilization of regional water resources,to prevent and mitigate glacier-related disasters.This study maps the current(2020)distribution of glacier boundaries across the Kaidu-Kongque river basin,south slope of Tianshan Mountains,and monitors the spatial evolution of glaciers over five time periods from 2000-2020 through thresholded band ratios approach,using 25 Landsat images at 30 m resolution.In addition,this study attempts to understand the role of climate characteristics for variable response of glacier area.The results show that the total area of glaciers was 398.21 km^(2)in 2020.The glaciers retreated by about 1.17 km^(2)/a(0.26%/a)from 2000 to 2020.The glaciers were reducing at a significantly rapid rate between 2000 and 2005,a slow rate from 2005 to 2015,and an accelerated rate during 2015-2020.The meteorological data shows slight increasing trends of mean annual temperature(0.02℃/a)and annual precipitation(2.07 mm/a).The correlation analysis demonstrates that the role of temperature presents more significant correlation with glacier recession than precipitation.There is a temporal hysteresis in the response of glacier change to climate change.Increasing trend of temperature in summer proves to be the driving force behind the Kaidu-Kongque basin glacier recession during the recent 20 years.

Remotely sensed estimation and mapping of soil moisture by eliminating the effect of vegetation cover

Soil moisture(SM), which plays a crucial role in studies of the climate, ecology, agriculture and the environment, can be estimated and mapped by remote sensing technology over a wide region. However, remotely sensed SM is constrained by its estimation accuracy, which mainly stems from the influence of vegetation cover on soil spectra information in mixed pixels. To overcome the low-accuracy defects of existing surface albedo method for estimating SM, in this paper, Qinghai Lake Basin, an important animal husbandry production area in Qinghai Province, China, was chosen as an empirical research area. Using the surface albedo computed from moderate resolution imaging spectroradiometer(MODIS) reflectance products and the actual measured SM data, an albedo/vegetation coverage trapezoid feature space was constructed. Bare soil albedo was extracted from the surface albedo mainly containing information of soil, vegetation, and both albedo models for estimating SM were constructed separately. The accuracy of the bare soil albedo model(root mean square error=4.20, mean absolute percent error=22.75%, and theil inequality coefficient=0.67) was higher than that of the existing surface albedo model(root mean square error=4.66, mean absolute percent error=25.46% and theil inequality coefficient=0.74). This result indicated that the bare soil albedo greatly improved the accuracy of SM estimation and mapping. As this method eliminated the effect of vegetation cover and restored the inherent soil spectra, it not only quantitatively estimates and maps SM at regional scales with high accuracy, but also provides a new way of improving the accuracy of soil organic matter estimation and mapping.

Moraine-dammed glacial lake changes during the recent 40 years in the Poiqu River Basin,Himalayas

Glacier retreat is not only a symbol of temperature and precipitation change, but a dominating factor of glacial lake changes in alpine regions, which are of wide concern for high risk of potential outburst floods. Of all types of glacial lakes, moraine-dammed lakes may be the most dangerous to local residents in mountain regions. Thus, we monitored the dy- namics of 12 moraine-dammed glacial lakes from 1974 to 2014 in the Poiqu River Basin of central west Himalayas, as well as their associated glaciers with a combination of remote sensing, topographic maps and digital elevation models （DEMs）. Our results indicate that all monitored moraine-dammed glacial lakes have expanded by 7.46 km2 in total while the glaciers retreated by a total of 15.29 km2 correspondingly. Meteorological analysis indicates a warming and drying trend in the Nyalam region from 1974 to 2014, which accelerated glacier retreat and then augmented the supply of moraine-dammed glacial lakes from glacier melt. Lake volume and water depth changed from 1974 to 2014 which indicates that lakes Kangxico, Galongco, and Youmojanco have a high potential for outburst floods and in urgent need for continuous moni- toring or artificial excavation to release water due to the quick increase in water depths and storage capacities. Lakes Jialongco and Cirenmaco, with outburst floods in 1981 and 2002, have a high potential risk for outburst floods because of rapid lake growth and steep slope gradients surrounding them.

Evidence for Accelerating Glacier Ice Loss in the Takht' e Solaiman Mountains of Iran from 1955 to 2010

This study reports on the clean ice area and surface elevation changes of the Khersan and Merjikesh glaciers in the north of Iran between 1955 and 2010 based on several high to medium spatial resolution remote sensing data.The object-oriented classification technique has been applied to nine remote sensing images to estimate the debris-free areas.The satellite-based analysis revealed that the clean ice areas of Khersan and Merjikesh glaciers shrank since 2010 with an overall area decrease of about 45% and 60% respectively.It means that the dramatic proportions of 1955 glaciers surface area are covered with debris during the last five decades.Although the general trend is a clean ice area decrease,some advancement is observed over the period of 1997-2004.During 1987-1991 the maximum decrease in the clean ice area was observed.However,the clean ice area had steadily increased between 1997 and 2010.To quantify the elevation changes besides the debris-free change analysis,several Digital Elevation Models(DEMs) were extracted from aerial photo(1955),topographic map(1997),ASTER image(2002) and Worldview-2 image(2010) and after it a 3-D Coregistration and a linear relationship adjustments techniques were used to remove the systematic shifts and elevation dependent biases.Unlike the sinusoidal variation of our case studies which was inferred from planimetric analysis,the elevation change results revealed that the glacier surface lowering has occurred during 1955-2010 continuously without any thickening with the mean annual thinning of about 0.4 ± 0.04 m per year and 0.3 ± 0.026 m per year for Khersan and Merjikesh glaciers,respectively.The maximum thinning rate has been observed during 1997-2002(about 1.1 ± 0.09 per year and 0.96 ± 0.01 mper year,respectively),which was compatible partially with debris-free change analysis.The present result demonstrates that although in debris-covered glaciers clean ice area change analysis can illustrate the direction of changes(retreat or advance),due to the high uncertainty in glacier area delineation in such glaciers,it cannot reveal the actual glacier changes.Thus,both planimetric and volumetric change analyses are very critical to obtain accurate glacier variation results.

Application of hydrological models in a snowmelt region of Aksu River Basin

This study simulated and predicted the runoff of the Aksu River Basin, a typical river basin supplied by snowmelt in an arid mountain region, with a limited data set and few hydrological and meteorological stations. Two hydrological models, the snowmelt-runoff model （SRM） and the Danish NedbФr-AfstrФmnings rainfall-runoff model （NAM）, were used to simulate daily discharge processes in the Aksu River Basin. This study used the snow-covered area from MODIS remote sensing data as the SRM input. With the help of ArcGIS software, this study successfully derived the digital drainage network and elevation zones of the basin from digital elevation data. The simulation results showed that the SRM based on MODIS data was more accurate than NAM. This demonstrates that the application of remote sensing data to hydrological snowmelt models is a feasible and effective approach to runoff simulation and prediction in arid unguaged basins where snowmelt is a major runoff factor.

巢湖流域土地利用碳排放时空变化及影响因素研究

文章基于夜间灯光数据估测巢湖流域土地利用碳排放量,从县域尺度上分析土地利用碳排放时空分布特征及空间相关性,探究其影响因素作用机理。结果表明:2012—2018年,巢湖流域土地利用特征较为显著,主要以耕地为主,建设用地和林地次之,水域、草地和未利用地较少;2012—2018年,巢湖流域碳源主要集中于合肥市区、肥东县和肥西县,碳汇主要集中于舒城县、巢湖市和庐江县,土地利用净碳排放总体呈增长趋势,且存在着显著的空间正相关关系;区域投资、经济发展、人口规模和土地利用结构对巢湖流域土地利用碳排放都有较大影响,且双因子交互作用均超过单个指标影响。研究结果可为制定合理的区域碳排放优化方案提供参考。

2001—2021年巢湖流域植被覆盖时空变化及驱动分析

基于2001—2021年Landsat遥感数据,研究巢湖流域植被覆盖多年变化,利用时空地理加权模型探讨地形、气候及人类活动的驱动影响。结果表明:(1)流域内平均植被覆盖度0.75,近20 a总体呈增加趋势,增速0.12%/a;2009年前,呈下降趋势,2009年后,呈增加趋势。(2)流域内89.79%的区域植被覆盖度高于0.6,不同土地利用的植被覆盖度为林地>旱作农田>稀疏植被>灌溉农田>城市建成区>湿地,湿地受蓄水排涝功能的影响,植被覆盖度相对较低。(3)近20 a,34.78%的区域植被覆盖度发生变化,以增加趋势为主,面积占比62.73%,集中在合肥市老城区、山区林地、沿江北岸平原地带以及环巢湖湿地区域,政策上的生态环境保护和流域治理对植被覆盖产生正影响成效显著;减少趋势发生在城市外围和部分耕地区域,体现城镇化建设、耕地种植模式等人类活动对植被覆盖的负影响,对于引江济淮(派河—东淝河)段施工沿线和柘皋河流域植被覆盖度减少,应值得关注。(4)2010年前,地形因素的影响逐年降低,气候作用逐年增加,2010年后,地形因素持续增加并成为主要因素。(5)人类活动对植被覆盖的影响程度整体呈增强趋势,生态环境得到改善,增强幅度为0.013%/(10 a)。

基于长时序稠密遥感数据分析黄河流域大中型湖库水域面积动态变化特征

黄河流域在我国经济社会发展和生态安全中具有重要地位。但从全流域的角度,基于长时序稠密遥感数据对黄河流域大中型湖库开展的研究却较少。本文基于MODIS 8天合成数据,提取了2000—2020年黄河流域大中型湖库长时序的水域信息,分析其时空变化特征,结果表明:从月际变化看,3—5月为水域面积第一个快速增长时期,6—10月为第二个增长时期,在10月达到最大值,10月之后逐渐下降,至次年2月达到最小值;从年际变化看,近20年上、中、下游湖库水域面积均呈现增长趋势,其中上游地区对全流域面积增长的贡献度最大,中游次之;湖库水域空间分布不均衡,上、中、下游近20年湖库水域面积平均占比分别为69.27%、25.02%、5.72%。

Simulation and construction of the glacier mass balance in the Manas River Basin,Tianshan,China from 2000 to 2016

The glacier mass balance(GMB)is an important link between climate and water resources and has remarkable regulatory functions in river runoff.To simulate changes of the GMB and to analyze the recharge rates of glacier meltwater to runoff in the Manas River Basin(MRB)during 2000-2016,MOD11C3,TRMM 3B43 and other multi-source remote sensing data were used to drive the degree-day model.The results showed that:(1)the accuracy of the remote sensing meteorological data can be corrected effectively by constructing the temperature and precipitation inversion models,and the characteristics of glacial climate can be finely described through downscaling.The average annual temperature was-7.57°C and the annual precipitation was 410.71 mm in the glacier area of the MRB.The zone at an altitude of about 4200 m was a severe climate change zone,and above and below that zone,the temperature drop rates were-0.03°C/100 m and-0.57°C/100 m,respectively,while precipitation gradients were-2.66 mm/100 m and 4.89 mm/100 m,respectively.(2)The overall GMB was negative with a cumulative GMB of up to-9811.19 mm w.e.and the average annual GMB fluctuated between-464.85 and-632.19 mm w.e.Besides,the glacier melted slowly during 2000-2002 and 2008-2010,but rapidly for 2002-2008 and 2010-2016,while the most serious loss of the glacier occurred in 2005-2009.Moreover,the vertical changes of the GMB increased at 244.83 mm w.e./100 m in the ablation zone but only at 18.77 mm w.e./100 m in the accumulation zone.(3)The intraannual runoff strongly responded to the change of the GMB especially in July and August when the loss of the GMB accounted for 75.4%of the annual loss,and when runoff accounted for 55.1%of the annual total.Due to differences in the annual precipitation and snow meltwater outside the glacier,the interannual glacier meltwater recharge rates fluctuated between 19%and 31%.The recharge rate of glacier meltwater to runoff in the MRB was close to that for other basins in the Tianshan Mountains,which may be used as a basis to confirm the reliability of the estimated GMB results.Furthermore,based on the present findings,it is recommended that the research community pursue studies on the GMB in other alpine river basins.

2010—2019年间洞庭湖流域生态环境状况时空动态特征及影响因素

洞庭湖流域是长江中下游重要生态区,开展其生态环境状况定量监测与评价是进行区域生态保护、修复及治理的先决条件。该文采用2010—2019年MODIS遥感数据产品,基于绿度、湿度、干度和热度4个生态指标构建了洞庭湖流域遥感生态环境指数(remote sensing ecological index,RSEI),并在此基础上研究了流域生态环境状况时空动态特征及其影响因素。结果表明:①2010—2019年洞庭湖流域绿度指标呈增长趋势,湿度指标呈下降趋势,而干度和热度指标变化较为平稳;②洞庭湖流域整体生态环境状况较好,RSEI多年均值为0.58,并呈波动增长,空间上则表现为西部优于东部、四周优于中部的分布格局;③降水、气温、高程以及土地覆盖与RSEI均具有较强相关性。其中,林地RSEI(0.65)最高,建筑用地RSEI(0.31)最低;在流域2种主要土地转化类型中(草地→林地、耕地→草地),“草地→林地”转化有助于促进区域生态环境(ΔRSEI=0.0025,贡献率为46.3%),而后者则有可能导致生态环境恶化(ΔRSEI=-0.0004,贡献率为44.44%)。研究结果有助于深刻把握流域生态环境时空特征及其内在驱动机制,辅助开展科学的土地规划与生态环境治理,因而具有较强的理论与实践意义。

基于多源遥感数据的洞庭湖流域时空演变研究

近年来,洞庭湖流域的生态环境面临巨大的压力,主要原因包括自然灾害和人类不合理的开发利用。正确获取流域时空演变趋势对于保护和建设洞庭湖流域的生态环境至关重要。文章基于2017—2021年遥感数据,采用NDWI水体指数阈值法(标准化差异水体指数),分析了洞庭湖在此期间的湖泊流域面积变化趋势,研究了流域重心的迁移趋势,探讨了流域关键问题和脆弱环节。结果表明,大通湖在2017年至2021年3月下旬期间水域变化不大,保持在稳定状态。通江湖泊水域面积变化相对比较大,尤其2019年相比2018年呈断崖式萎缩,由2018年的863 km^(2)萎缩到2019年的648.02 km^(2),减幅214.98 km^(2)。影响湖泊演变的气象因素中,降雨与气温相关性最高。该研究成果可为洞庭湖流域可持续发展的治理措施的制定和科学规划提供重要参考依据。

洱海流域常用非同源LULC产品一致性分析和精度评估

高精度的土地利用/土地覆盖(land use/land cover,LULC)信息对于应对当前的环境挑战至关重要。尽管全球高分辨率LULC数据产品蓬勃发展,但多源数据存在不同程度的不确定性,在区域尺度如何选择适宜的LULC产品成为各领域应用中的难题。该研究以洱海流域为例,结合国土变更调查数据,通过公里网格采样、实地调查、高分影像解译获取了2947个验证样本,对7套常用非同源LULC数据产品进行了面积、空间一致性、混淆程度分析和精度评估,定量分析了LULC产品制图精度的影响因素以及各数据集优缺点与适用性。结果表明:1)洱海流域8套土地覆被数据集中高一致性区域、中一致性、低一致性区域分别占总面积的64.13%、34.00%和1.87%,且均存在对灌木和草地的错分、混淆严重的现象,不同产品对不同区域、不同地类的刻画能力差异明显。2)各LULC产品的总体精度在69.5%~81.1%之间。相较其他开源LULC数据,ESA_WC提供了较好的数据质量和空间细节,尤其对于破碎景观下的耕地识别。3)香农多样性指数对洱海流域土地覆被空间一致性差异影响最大,其次是灌木林地占比,而高程标准差、斑块面积大小和云覆盖频率的影响并不明显。对洱海流域土地覆盖进行全要素研究时,10 m分辨率数据可选择总体精度最高的ESA_WC;30 m分辨率数据中CLCD数据的精度较高,但相比其他产品显著低估了不透水面面积,不适用于城市扩张等研究。针对特定的应用需求,可参考该文提供的7种LULC产品的分类精度和优缺点,有针对性地进行数据选择。

基于遥感影像的鄱阳湖采砂时空分布及对湖盆形态的影响研究

研究通过使用Landsat卫星遥感数据和水文资料统计数据,总结出鄱阳湖1999—2021年的采砂船时空分布规律,分析了采砂活动对鄱阳湖水文泥沙平衡以及对湖盆形态变化的影响。方法上,研究采用中红外波段的黑白影像进行采砂船提取,并结合增强型水体指数突出水陆边界,再叠加出枯水期湖盆形态的变化。结果表明:①2000—2006年采砂船主要分布在鄱阳湖的北湖部分,2008年受禁采政策影响,采砂船数量骤减,2016年为采砂活动的高峰,其中政策调控是2000—2021年鄱阳湖采砂船时空分布和数量规模变化的主要因素;②人类采砂活动在一定程度上影响着鄱阳湖的水文泥沙平衡;③采砂活动导致鄱阳湖入江水道和松门山区域的滩地面积减少,而棠荫东南部区域滩地面积净增加约7.95 km^(2),主要原因是入湖支流泥沙扩散造成的淤积。研究不仅能够评估近年来对鄱阳湖采砂活动监管的成效,还可为类似水域的采砂活动监管及其效果评估提供参考。